The FINANCIAL -- The NDP report covers a 12-month period that ran through November of 2018 and shows total unit sales of smartwatches up 61 percent year over year. Corresponding dollar sales were up as well, jumping 51 percent over the same period. That equates to nearly $5 billion in sales, the firm said.

While NDP said Apple is the "clear market leader," sales of devices manufactured by Samsung and Fitbit are also outpacing the rest of the industry. The top three smartwatch makers combined account for 88 percent of the total market. Rankings might change in 2019 as small fashion and fitness-focused brands such as Fossil and Garmin angle to enlarge their piece of the pie.

In the U.S., 16 percent of adults now own a smartwatch, up from 12 percent in December 2017. With a 23 percent ownership rate, NDP credits the younger 18-year-old to 34-year-old market with pushing overall growth, but notes heart health features like those included in Apple Watch Series 4 could significantly boost smartwatch popularity in the older demographic in 2019.

Smart homes were also popular for users, with 15 percent of watch owners saying they use the devices to control their homes and automated devices.

Apple does not break out Apple Watch sales, but during its most recent investor conference call said revenue from "wearables, home and accessories" products reached $7.3 billion., up 33 percent year-on-year. CEO Tim Cook recently commented on the wearable sector's explosive growth over the past few quarters, saying category revenue is already more than 50 percent above iPod's all-time high.

"[I]f you take AirPods and the Watch separately, and you sort of back these up and align it to the launch date of iPod, as well, where all of them have a comparable amount of time, you would find that each one independently is four to six times ahead of where iPod was at a comparable period of time," Cook said.